“With the continuous increase of labor costs, it is an important direction of modern robotics research to use robots instead of human to do some repetitive and high-intensity labor. The handling robot needs the coordinated work of the rear wheel drive motor and the front wheel steering gear in the process of navigation and tracking.
With the continuous increase of labor costs, it is an important direction of modern robotics research to use robots instead of human to do some repetitive and high-intensity labor. The handling robot needs the coordinated work of the rear wheel drive motor and the front wheel steering gear in the process of navigation and tracking. The motor drive of the handling robot has its special application requirements, and the dynamic performance of the motor is required to be high. It can reach the specified position required for control at any time and stop the steering gear at any angle; the motor drive has a large torque variation range, both The high-speed, low-torque working environment of no-load smooth road operation also has full-load climbing operating conditions, and at the same time, it is also required to maintain a high operating efficiency. According to the above technical requirements, this paper selects the DC motor with mature control technology and easy to adjust the speed smoothly as the execution mechanism of the handling robot.
The power supply of the motor is provided by a 24V battery with a rated power of 240W, which is realized by a bridge circuit composed of four 75N75. 75N75 is a MOSFET power tube with a maximum voltage of 75V and a maximum current of 75A. The motor drive circuit is shown in Figure 2.
Q1, Q4 and Q2, Q3 respectively form two bridge circuits, which control the forward and reverse rotation of the motor respectively. When the high-end driven MOS tube is turned on, the source voltage and drain voltage are the same and equal to the power supply VCC, so to achieve normal driving of the MOS tube, the gate voltage is larger than VCC, which requires a special boost chip IR2103 . The PWM signal generated by the controller is input to the HIN pin, and the EN1 and EN2 output by the controller I/O port are used as enable signals. The output terminal HO can get a higher voltage than VCC, and the higher voltage value is exactly the voltage charged at both ends of the capacitor. The diode increases the turn-on speed, making the on-resistance of the 75N75 smaller and reducing the loss of the switch. At the same time, the two output ports HO and LO of IR2103 have an interlock function to prevent short-circuit caused by the direct connection of the upper and lower bridge arms of the motor due to software or hardware errors.
Design of overcurrent protection
The installation of overcurrent protection in the motor control system has two meanings: one is to prevent the motor from being overloaded or blocked when the motor is running normally, which will cause excessive armature winding current to damage the motor or even cause a fire; the other is to prevent the motor from being overloaded or blocked. When the shoulder is moved, the starting current is very large, and it is often impossible to start directly. It is necessary to wait for the excitation winding to gradually establish a magnetic field before normal operation, and it is hoped that the motor should move at the fastest speed possible. With overcurrent protection to chop the current, the motor can be started safely and quickly. The schematic diagram of overcurrent protection is shown in Figure 3.
The phase current of the motor is converted into the voltage signal Vtext through the constantan wire, and the analog quantity AD1 amplified by the operational amplifier is sent to the A/D conversion module of the controller, and the digital quantity EVA after comparison by the voltage comparator is sent to the controller. External interrupt port. According to the control requirements of the front-wheel steering servo and rear-wheel drive motor of the handling robot, the STM32F107 with Cortex-M3 as the core is used as the main controller, and the embedded real-time operating system μC/OS-II is used to divide the program into startup tasks, motor There are relatively independent tasks such as speed control tasks and steering gear control tasks, and the priority of each task is set. The system can better realize the motion control of the handling robot.